Energy Storage System

This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0045550 filed in the Korean Intellectual Property Office on Apr. 6, 2023, the entire content of which is incorporated herein by reference.

Embodiments disclosed herein relate to an energy storage system.

An energy storage system (ESS) is a system that links new renewable energy, batteries storing power, and existing grid power. Recently, with the spread of smart grids, the expansion of new and renewable energy, and the emphasis on the efficiency and stability of power grids, demands for energy storage systems are increasing for power supply, demand control, and power quality improvement. The energy storage system has different output and capacity according to the purpose of use. To constitute a large-volume energy storage system, a plurality of battery systems are connectable to one another.

The energy storage system is evolving from an alternating current (AC)-coupled energy storage system into a direct current (DC)-coupled energy storage system. In the DC-coupled ESS system, a battery system and a grid have different voltage levels and different voltage types, a DC voltage for the battery system and an AC voltage for the grid. Thus, a DC-DC converter and a DC-AC inverter which are power conversion devices are essentially required between the battery system and the grid.

Among them, the DC-DC converter is mounted on every battery cell or battery module to function as the DC-DC converter for the whole system, and a structure having various advantages such as cell balancing, defective cell blocking, etc., is being developed. In this way, power consumption of the DC-DC converter in the energy storage system may be reduced, but power consumption occurring in the DC-AC inverter is still a problem to be overcome.

Embodiments disclosed herein provide an energy storage system capable of generating an AC voltage by using a DC-DC converter at a stage of a battery cell, a battery module, or a battery pack.

Technical problems of the embodiments disclosed herein are not limited to the above-described technical problems, and other unmentioned technical problems would be clearly understood by one of ordinary skill in the art from the following description.

An energy storage system (ESS) includes a plurality of battery units, a plurality of direct current-direct current (DC-DC) converters respectively connected to the plurality of battery units to convert an input voltage from a connected battery unit into an output voltage, and a controller configured to control the plurality of DC-DC converters such that a summed voltage of output voltages of the plurality of DC-DC converters is an alternating current (AC) voltage.

In the energy storage system according to an embodiment disclosed herein, the plurality of DC-DC converters may be respectively connected to a positive electrode and a negative electrode of the plurality of battery units, and the summed voltage may be applied to a grid system connected to the energy storage system.

In the energy storage system according to an embodiment disclosed herein, the plurality of DC-DC converters may be configured to perform a bypass function that causes a magnitude of the output voltage of the connected battery unit to be 0 V, and the controller may be further configured to control the plurality of DC-DC converters by using the bypass function such that the summed voltage of output voltages of the plurality of DC-DC converters is an AC voltage.

In the energy storage system according to an embodiment disclosed herein, the controller may be further configured to control the plurality of DC-DC converters to perform the bypass function according to a designated period.

In the energy storage system according to an embodiment disclosed herein, the plurality of DC-DC converters may be configured to perform a rise control function for causing the output voltage of the connected battery unit to be a voltage rising based on a designated slope and/or a drop control function for causing the output voltage to be a voltage dropping based on the designated slope, and the controller may be further configured to control the plurality of DC-DC converters by using the rise control function and the drop control function such that the summed voltage of output voltages of the plurality of DC-DC converters is an AC voltage.

In the energy storage system according to an embodiment disclosed herein, the controller may be further configured to control the plurality of DC-DC converters such that the summed voltage has at least one of a magnitude, a phase, and a frequency corresponding to a required AC voltage of the grid system.

In the energy storage system according to an embodiment disclosed herein, the controller may be further configured to control the plurality of DC-DC converters based on a state of the plurality of battery units.

The energy storage system according to an embodiment disclosed herein may further include at least one battery management system (BMS) configured to manage the state of the plurality of battery units, in which the controller may be further configured to obtain state data of the plurality of battery units from the at least one BMS and determine the state of the plurality of battery units based on the state data.

In the energy storage system according to an embodiment disclosed herein, the state data of the plurality of battery units may include data related to at least one of a voltage, a current, a temperature, a state of charge (SOC), and a state of health (SOH) of the plurality of battery units.

In the energy storage system according to an embodiment disclosed herein, each of the plurality of battery units may include a battery cell, a battery module, a battery pack, or a battery rack.

An energy storage system (ESS) includes a plurality of battery units; and a plurality of direct current-direct current (DC-DC) converters each having an input terminal and electrically connected to a positive electrode and a negative electrode of the plurality of battery units, respectively, to convert an input voltage from a connected battery unit into an output voltage, and connection units respectively between the plurality of battery units and the plurality of DC-DC converters are connected to each other in series, and the plurality of DC-DC converters and a grid system are electrically connected such that at least a part of a summed voltage of output voltages of the plurality of DC-DC converters is applied to the grid system.

A positive output terminal of a first DC-DC converter among the plurality of DC-DC converters may be electrically connected to a positive input terminal of the grid system, and a negative output terminal of a second DC-DC converter among the plurality of DC-DC converters is electrically connected to a negative input terminal of the grid system, and positive output terminals of DC-DC converters other than the first DC-DC converter and the second DC-DC converter among the plurality of DC-DC converters are electrically connected to a negative output terminal of an adjacent DC-DC converter.

The energy storage system may include a storage element electrically connected to the positive output terminal of the first DC-DC converter and the negative output terminal of the second DC-DC converter.

th th th th The energy storage system may include a switch configured to selectively connect a positive output terminal of a first DC-DC converter among a plurality of 2N DC-DC converters or a negative output terminal of a 2NDC-DC converter among the plurality of DC-DC converters to a positive input terminal of the grid system, wherein N is a natural number, and positive output terminals of DC-DC converters other than the first DC-DC converter and the 2NDC-DC converter among the plurality of DC-DC converters are electrically connected to a negative output terminal of an adjacent DC-DC converter, and a negative output terminal of an NDC-DC converter among the plurality of DC-DC converters is electrically connected to a positive output terminal of (N+1)DC-DC converter among the plurality of DC-DC converters and a negative input terminal of the grid system.

th The energy storage system can include a storage element electrically connected to a first end of the switch, and the switch is electrically connected to the grid system and the negative output terminal of the NDC-DC converter through the storage element.

According to embodiments disclosed herein, an AC voltage required for a grid system may be generated merely with a DC-DC converter, thereby omitting a DC-AC inverter in an energy storage system and thus providing advantages in terms of power efficiency, power density, and temperature when compared to an existing energy storage system.

Moreover, various effects recognized directly or indirectly from the disclosure may be provided.

Hereinafter, various embodiments of the present disclosure will be disclosed with reference to the accompanying drawings. However, the description is not intended to limit the present disclosure to particular embodiments, and it should be construed as including various modifications, equivalents, and/or alternatives according to the embodiments of the present disclosure.

It should be appreciated that various embodiments of the present document and the terms used therein are not intended to limit the technological features set forth herein to particular embodiments and include various changes, equivalents, or replacements for a corresponding embodiment. With regard to the description of the drawings, similar reference numerals may be used to refer to similar or related elements. It is to be understood that a singular form of a noun corresponding to an item may include one or more of the things, unless the relevant context clearly indicates otherwise.

st nd As used herein, each of such phrases as “A or B,” “at least one of A and B,” “at least one of A or B,” “A, B, or C,” “at least one of A, B, and C,” and “at least one of A, B, or C,” may include any one of, or all possible combinations of the items enumerated together in a corresponding one of the phrases. Such terms as “1”, “2” “first”, “second”, “A”, “B”, “(a)”, or “(b)” may be used to simply distinguish a corresponding component from another, and does not limit the components in other aspect (e.g., importance or order), unless mentioned otherwise.

Herein, it is to be understood that when an element (e.g., a first element) is referred to, with or without the term “operatively” or “communicatively”, as “connected with”, “coupled with”, or “linked with”, or “coupled to” or “connected to” to another element (e.g., a second element), it means that the element may be connected with the other element directly (e.g., wiredly), wirelessly, or via a third element.

According to various embodiments, each component (e.g., a module or a program) of the above-described components may include a single entity or multiple entities, and some of the multiple entities may be separately disposed in different components. According to various embodiments, one or more of the above-described components may be omitted, or one or more other components may be added. Alternatively or additionally, a plurality of components (e.g., modules or programs) may be integrated into a single component. In such a case, according to various embodiments, the integrated component may still perform one or more functions of each of the plurality of components in the same or similar manner as they are performed by a corresponding one of the plurality of components before the integration. According to various embodiments, operations performed by the module, the program, or another component may be carried out sequentially, in parallel, repeatedly, or heuristically, or one or more of the operations may be executed in a different order or omitted, or one or more other operations may be added.

1 FIG. is a block diagram showing conventional energy storage system and grid system.

1 FIG. 110 120 111 112 113 Referring to, a conventional energy storage systemis connected to a grid system, and includes a battery unit, a direct current-direct current (DC-DC) converter, and a DC-alternating current (AC) inverter.

111 1 FIG. A minimum unit of a battery that stores power in an energy storage system (ESS) is generally a battery cell. A serial/parallel combination of battery cells constitutes a battery module, and a plurality of battery modules constitute a battery pack or a battery rack. The battery unitshown inmay be a battery pack or a battery rack.

110 120 120 120 110 120 The conventional energy storage systemmay transmit power to the grid system(in case of discharging) or receive power from the grid system(in case of charging). Herein, the grid systemrequires AC power, such that power transmitted between the energy storage systemand the grid systemis AC power.

110 111 112 113 120 110 120 113 112 111 More specifically, in case of discharging, the conventional energy storage systemconverts DC output power of the battery unitinto AC power through the DC-DC converterand the DC-AC inverterand transmits the AC power to the grid system. In case of charging, the conventional energy storage systemconverts AC power transmitted from the grid systeminto DC power through the DC-AC inverterand the DC-DC converterand transmits the DC power to the battery unit.

110 113 113 113 That is, the conventional energy storage systemessentially requires the DC-AC inverterfor power transmission/reception described above. However, due to such a structure, while power passes through the DC-AC inverter, power consumption occurs, lowering power efficiency, or due to heat emission caused by inversion of the DC-AC inverter, the temperature of the entire system excessively increases.

2 FIG. is a block diagram showing an energy storage system and a grid system, according to an embodiment.

2 FIG. 200 260 200 260 200 260 200 260 Referring to, an energy storage systemmay be connected to a grid system. According to an embodiment, the energy storage systemand the grid systemmay transmit and receive AC power. For example, during discharging, the energy storage systemmay transmit AC power to the grid system. In another example, during charging, the energy storage systemmay receive AC power from the grid system.

200 210 220 230 240 212 222 232 242 250 200 2 FIG. 2 FIG. According to an embodiment, the energy storage systemmay include a plurality of battery units,,, and, a plurality of DC-DC converters,,, and, and a controller. According to an embodiment, the energy storage systemshown inmay further include at least one component (e.g., a battery system controller (BSC), an energy management system (EMS), or a power management system (PMS)) in addition to components shown in.

200 210 220 230 240 2 FIG. A battery that stores power in the energy storage systemis generally implemented in such a way that a plurality of battery modules having a plurality of battery cells connected in series/in parallel constitute a battery pack or a battery rack and a plurality of battery packs or a plurality of battery racks constitute a battery bank. Each of the plurality of battery units,,, andshown inmay be a battery cell, a battery module, a battery pack, or a battery rack.

210 220 230 240 According to an embodiment, the plurality of battery units,,, andmay be connected in series or in parallel.

211 221 231 241 210 220 230 240 211 221 231 241 210 220 230 240 211 221 231 241 210 220 230 240 211 221 231 241 210 220 230 240 According to an embodiment, battery management systems (BMSs),,, andmay be respectively installed in the plurality of battery units,,, and. The BMSs,,, andmay respectively manage states of the battery units,,, andmanaged by them. According to an embodiment, the BMS,,, ormay monitor a voltage, a current, and/or a temperature of the battery unit,,, orand calculate an SOC and/or an SOH based on a monitoring result. The BMS,,, ormay control charging/discharging based on the state of the battery unit,,, or.

211 221 231 241 210 220 230 240 250 According to an embodiment, the BMS,,, ormay transmit state data related to at least one of the voltage, the current, the temperature, the SOC, or the SOH of the battery unit,,, orto the controller.

212 222 232 242 210 220 230 240 212 210 222 220 232 230 242 240 th th According to an embodiment, the plurality of DC-DC converters,,, andmay be respectively connected to the plurality of battery units,,, and. For example, the first DC-DC convertermay be connected to the first battery unit, the second DC-DC convertermay be connected to the second battery unit, the third DC-DC convertermay be connected to the third battery unit, and the NDC-DC convertermay be connected to the Nbattery unit(N is a natural number of 4 or greater).

212 222 232 242 260 212 222 232 242 260 212 222 232 242 260 212 222 232 242 260 According to an embodiment, the plurality of DC-DC converters,,, andmay be directly or indirectly connected to the grid system. A summed voltage of output voltages of the plurality of DC-DC converters,,, andmay be applied to the grid systemthrough the connection. According to an embodiment, a predetermined filter may be connected between the plurality of DC-DC converters,,, andand the grid system. In this case, the predetermined filter may be implemented with an AC transformer that transforms the summed voltage of the output voltages of the plurality of DC-DC converters,,, andinto a required voltage of the grid system. For example, the predetermined filter may transform the summed voltage such that a median voltage value of the AC voltage that is the summed voltage is 0 V.

212 222 232 242 212 222 232 242 212 222 232 242 According to an embodiment, the plurality of DC-DC converters,,, andmay convert an input voltage into an output voltage of a designated magnitude. For example, the DC-DC converter,,, ormay be implemented as a converter of various types such as a full-bridge converter, a half-bridge converter, a flyback converter, etc. The DC-DC converter,,, ormay include a separate controller, an input switching set, a primary coil, a secondary coil, an output switching set, and a capacitor.

212 222 232 242 210 220 230 240 260 212 222 232 242 210 220 230 240 212 222 232 242 260 260 210 220 230 240 212 222 232 242 260 212 222 232 242 210 220 230 240 According to an embodiment, the plurality of DC-DC converters,,, andmay be bidirectional converters. For example, conversion may be performed from the plurality of battery units,,, andto the grid system, and an input of the plurality of DC-DC converters,,, andmay be connected to the plurality of battery units,,, and, and an output of the plurality of DC-DC converters,,, andmay be connected to the grid system. In another example, when conversion is performed from the grid systemto the plurality of battery units,,, and, the input of the plurality of DC-DC converters,,, andmay be connected to the grid system, and the output of the plurality of DC-DC converters,,, andmay be connected to the plurality of battery units,,, and.

212 222 232 242 According to an embodiment, the plurality of DC-DC converters,,, andmay be configured to perform a particular function.

212 222 232 242 210 220 230 240 According to an embodiment, the particular function may include a bypass function such that a magnitude of an output voltage is 0 V. The DC-DC converter,,, ormay block power output from the connected battery unit,,, orby performing the bypass function.

According to an embodiment, the particular function may include a rise control function for causing the output voltage to be a voltage rising based on a designated slope and/or a drop control function for causing the output voltage to be a voltage dropping based on the designated slope.

250 According to an embodiment, the controllermay include a central processing unit, an application processor, a graphic processing unit, a neural processing unit (NPU), an image signal processor, a sensor hub processor, or a communication processor.

250 211 221 231 241 212 222 232 242 200 250 In an embodiment, the controllermay execute software to control at least one other components (e.g., the BMS,,, or, the DC-DC converter,,, or) of the energy storage systemconnected to the controllerand process or compute various data.

250 212 222 232 242 212 222 232 242 250 212 222 232 242 260 According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andsuch that the summed voltage of the output voltages of the plurality of DC-DC converters,,, andis an AC voltage. According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andsuch that the summed voltage has a magnitude, a phase, and/or a frequency corresponding to a required AC voltage of the grid system.

250 212 222 232 242 250 212 222 232 242 250 212 222 232 242 According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andby using the bypass function such that the summed voltage is an AC voltage. The controllermay control the number of DC-DC converters,,, andfrom which a voltage is output, through the bypass function. The controllermay also control a magnitude of the output voltage of the DC-DC converters,,, orfrom which a voltage is output.

250 212 222 232 242 According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andto perform the bypass function for a designated time.

250 212 222 232 242 212 222 232 242 260 260 According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andto perform the bypass function according to a designated period. Herein, the designated period may be set to be the same or different for the plurality of DC-DC converters,,, and. The designated period may be set based on a magnitude, a phase, and/or a frequency corresponding to the required AC voltage of the grid system. For example, to cause the summed voltage to be the required AC voltage, the designated period may be set to be shorter than the period of the required AC voltage of the grid system.

250 212 222 232 242 According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andto sequentially perform the bypass function in a designated order.

212 222 232 242 250 212 222 232 242 260 As such, by controlling the magnitude of the DC output voltage of the plurality of DC-DC converters,,, and, the controllermay control the plurality of DC-DC converters,,, andsuch that the summed voltage is an AC voltage (specifically, the required AC voltage of the grid system).

250 212 222 232 242 250 212 222 232 242 260 250 260 According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andby using a rise control function and a drop control function such that the summed voltage is an AC voltage. For example, the controllermay control the DC-DC converter,,, orto output a rising or dropping voltage based on a designated slope. Herein, the designated slope may be set based on a magnitude, a phase, and/or a frequency corresponding to the required AC voltage of the grid system. The controllermay transmit an AC voltage in a gentle form to the grid systemthrough the rise control function and the drop control function.

250 212 222 232 242 250 212 222 232 242 According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andby using all of the bypass function, the rise control function, and the drop control function such that the summed voltage is an AC voltage. For example, the controllermay control at least some of the plurality of DC-DC converters,,, andto perform the bypass function and the others to perform the rise control function and/or the drop control function.

250 212 222 232 242 210 220 230 240 According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andbased on the state of the plurality of battery units,,, and.

250 210 220 230 240 211 221 231 241 250 210 220 230 240 250 210 220 230 240 According to an embodiment, the controllermay obtain state data of the plurality of battery units,,, andfrom at least one BMS,,, and/or. The controllermay determine the state of the plurality of battery units,,, andbased on the obtained state data. For example, the controllermay determine the state of the plurality of battery units,,, andas an abnormal state or a normal state.

250 212 222 232 242 250 212 222 232 242 212 222 232 242 According to an embodiment, the controllermay control the plurality of DC-DC converters,,, andbased on the determined state. For example, the controllermay control the DC-DC converter,,, orconnected to the battery unit,,, ordetermined to be in the abnormal state to perform the bypass function.

250 210 220 230 240 210 220 230 240 250 210 220 230 240 210 220 230 240 For example, the controllermay determine the battery unit,,, orto be in the abnormal state when the output voltage, the SOC, or the SOH of the battery unit,,, oris less than or equal to a designated level. In another example, the controllermay determine the battery unit,,, orto be in the abnormal state when the temperature of the battery unit,,, oris greater than or equal to a designated temperature.

3 FIG. is a view for describing a connection structure between a battery unit and a DC-DC converter in an energy storage system, according to an embodiment.

300 360 200 260 3 FIG. 2 FIG. An energy storage systemand a grid systemshown inmay respectively have the same configurations as the energy storage systemand the grid systemshown in.

3 FIG. 2 FIG. 312 322 332 342 310 320 330 340 312 322 332 342 310 320 330 340 250 300 310 320 330 340 Referring to, a plurality of DC-DC converters,,, andmay be respectively connected to positive electrodes and negative electrodes of a plurality of battery units,,, and. That is, the plurality of DC-DC converters,,, andmay be respectively connected to convert output voltages of the plurality of battery units,,, and. Thus, a controller (e.g., the controllerof) of the energy storage systemmay separately control the output voltage of each of the plurality of battery units,,, and.

310 320 330 340 312 322 332 342 312 342 1 312 360 342 360 312 322 332 342 1 360 th According to an embodiment, connection units between the plurality of DC-DC converters,,, andand the plurality of battery units,,, andmay be connected to each other in series. In a corresponding embodiment, a positive output terminal of the first DC-DC converterand a negative output terminal of the NDC-DC convertermay be connected to each other through a storage element Cserving to store energy. The positive output terminal of the first DC-DC convertermay be connected to a positive input terminal of the grid system, and the negative output terminal of the Nth DC-DC convertermay be connected to a negative input terminal of the grid system. With such a connection structure, the summed voltage of the output voltages of the plurality of DC-DC converters,,, andmay be stored in the storage element Cor may be applied to the grid system.

4 4 FIGS.A toC are views for describing an example in which a plurality of DC-DC converters in an energy storage system sequentially perform a specific function according to an embodiment. Herein, the specified function may include the bypass function, the rise control function, and/or the drop control function.

400 460 200 260 4 4 FIGS.A toC 2 FIG. An energy storage systemand a grid systemshown inmay respectively have the same configurations as the energy storage systemand the grid systemshown in.

4 FIG.A 412 412 422 432 442 422 432 442 460 420 430 440 410 422 432 442 Referring to, a first DC-DC converteramong a plurality of DC-DC converters,,, andmay perform the specified function, and the other DC-DC converters,, andmay not perform the specified function. When the specified function is the bypass function, the summed voltage applied to the grid systemmay be a summed voltage of voltages into which voltages output from the other battery units,, andthan the first battery unitare converted by the other DC-DC converters,, and.

4 FIG.B 412 422 432 442 412 432 422 442 460 420 440 410 430 422 442 Referring to, among the plurality of DC-DC converters,,, and, the first DC-DC converterand the third DC-DC convertermay perform the specified function, and the other DC-DC convertersandmay not perform the specified function. When the specified function is the bypass function, the summed voltage applied to the grid systemmay be a summed voltage of voltages into which voltages output from the other battery unitsandthan the first battery unitand the third battery unitare converted by the other DC-DC convertersand.

4 FIG.C 412 422 432 442 412 432 442 422 460 420 410 430 440 422 th th Referring to, among the plurality of DC-DC converters,,, and, the first DC-DC converter, the third DC-DC converter, and the NDC-DC convertermay perform the specified function, and the other DC-DC convertermay not perform the specified function. When the specified function is the bypass function, the summed voltage applied to the grid systemmay be a summed voltage of voltages into which a voltage output from the other battery unitthan the first battery unit, the third battery unit, and the Nbattery unitis converted by the other DC-DC converter.

400 400 400 250 400 400 2 FIG. As such, the controllermay control the plurality of DC-DC convertersto perform or not to perform the specified function such that the summed voltage of the output voltages of the plurality of DC-DC convertersis an AC voltage. More specifically, a controller (e.g., the controllerof) in the energy storage systemmay control the plurality of DC-DC convertersto perform or not to perform the specified function.

400 412 422 432 442 400 412 432 442 th 4 FIG.A 4 FIG.B 4 FIG.C In an embodiment, the energy storage systemmay control the plurality of DC-DC converters,,, andto sequentially perform the specified function in a designated order. For example, the energy storage systemmay control the first DC-DC converter, the third DC-DC converter, and the NDC-DC converterin that order (i.e., in order of,, and) to perform the specified function. This may be a control for generating a part of an AC voltage waveform in which a voltage drops. However, the designated order is not limited thereto and may be set variously such that the summed voltage is the required AC voltage.

5 FIG. is a view for describing a connection structure among a battery unit, a DC-DC converter, and a switch in an energy storage system, according to an embodiment.

500 590 200 260 5 FIG. 2 FIG. An energy storage systemand a grid systemshown inmay respectively have the same configurations as the energy storage systemand the grid systemshown in.

5 FIG. 500 510 520 530 540 550 560 570 580 512 522 532 542 552 562 572 582 2 Referring to, the energy storage systemmay include a plurality of battery units,,,,,,, and, a plurality of DC-DC converters,,,,,,, and, a switch SW, and a storage element C.

512 522 532 542 552 562 572 582 510 520 530 540 550 560 570 580 512 522 532 542 552 562 572 582 510 520 530 540 550 560 570 580 250 500 510 520 530 540 550 560 570 580 2 FIG. The plurality of DC-DC converters,,,,,,, andmay be respectively connected to positive electrodes and negative electrodes of the plurality of battery units,,,,,,, and. That is, the plurality of DC-DC converters,,,,,,, andmay be respectively connected to convert the output voltages of the plurality of battery units,,,,,,, and. With this connection structure, a controller (e.g., the controllerof) of the energy storage systemmay separately control the output voltage of each of the plurality of battery units,,,,,,, and.

510 520 530 540 512 522 532 542 550 560 270 580 552 562 572 582 542 th th th th th th th th th th th th According to an embodiment, connection units between the first battery unit, the second battery unit, the third battery unit, and the Nbattery unitand the first DC-DC converter, the second DC-DC converter, the third DC-DC converter, and the NDC-DC convertermay be connected to each other in series. According to an embodiment, connection units between the (N+1)battery unit, the (2N−2)battery unit, the (2N−1)battery unit, and the 2Nbattery unit, and the (N+1)DC-DC converter, the (2N−2)DC-DC converter, the (2N−1)DC-DC converter, and the 2NDC-DC convertermay be connected to each other in series. Herein, a negative output terminal of the NDC-DC converterand a positive output terminal of the (N+1)DC-DC converter may be connected to each other.

2 542 2 512 582 th th th According to an embodiment, an end of the storage element Cserving to store energy may be connected to the switch SW, and the other end may be connected to the negative output terminal of the NDC-DC converterand the positive output terminal of the (N+1)DC-DC converter. The switch SW may be configured to connect an end of the storage element Cto the positive output terminal of the first DC-DC converteror the negative output terminal of the 2NDC-DC converter.

512 512 522 532 542 590 582 552 562 572 582 1 590 th th th th th th With this connection structure, when the switch SW is in connection to the positive output terminal of the first DC-DC converter, a first summed voltage of output voltages of the first DC-DC converter, the second DC-DC converter, the third DC-DC converter, . . . , and the NDC-DC convertermay be stored in the storage element Cl or may be applied to the grid system. When the switch SW is in connection to the negative output terminal of the 2NDC-DC converter, a second summed voltage of output voltages of the (N+1)DC-DC converter, the (2N−2)DC-DC converter, the (2N−1)DC-DC converter, and the 2NDC-DC convertermay be stored in the storage element Cor may be applied to the grid system.

1 590 500 490 590 Herein, the first summed voltage and the second summed voltage stored in the storage element Cor applied to the grid systemmay have opposite directions. For example, the first summed voltage may have a positive value, and the second summed voltage may have a negative value. Thus, the energy storage systemmay control a median voltage value of an AC voltage applied to the grid systemto be 0 V without a separate filter. To this end, a predetermined period in which connection of the switch SW is changed may be set to ½ of a required AC voltage period of the grid system.

Terms such as “include”, “constitute” or “have” described above may mean that the corresponding component may be inherent unless otherwise stated, and thus should be construed as further including other components rather than excluding other components. All terms including technical or scientific terms have the same meanings as those generally understood by those of ordinary skill in the art to which the embodiments disclosed herein pertain, unless defined otherwise. The terms used generally like terms defined in dictionaries should be interpreted as having meanings that are the same as the contextual meanings of the relevant technology and should not be interpreted as having ideal or excessively formal meanings unless they are clearly defined in the present document.